Semiconductor devices primarily based on silicon, such as transistors, diodes, thyristors, and rectifiers, typically include a p-n junction between the p-type semiconductor and the n-type semiconductor. The p-n junction is subjected to higher voltage in reverse bias. At certain voltages, reverse leakage current becomes excessive and the device fails. The main contributor to the reverse leakage current of the p-n junction, is the surface leakage current occurring at the defects on the surface (i.e. periphery) of the p-n junction, especially at elevated operating temperatures and at elevated device voltages. Therefore, semiconductor devices often utilize a passivation layer covering the periphery of the p-n junction to provide low leakage current therefrom. In passivated p-n junctions, leakage current occurring at the interface layer between the passivation layer and silicon also contributes to the reverse leakage current.
Many conventional passivation techniques employ lead based glasses. However, lead is environmentally unfriendly and therefore undesirable. Although lead free ZnO—B2O3—SiO2 glasses have been advanced for high voltage devices, these glasses suffer from several difficulties, such as higher firing temperatures, excessive devitrification (i.e. crystallization of zinc-borates) causing insufficient negative surface charge density, and sometimes disadvantageously requiring the addition of some heavier alkali oxides, such as Cs2O, in order to fire at desired lower temperatures. Since alkali ions from these heavier alkali oxides can move across a thin layer of glass under high electric field during the application of high voltage, this movement of ions could cause instability for high voltage devices.
As such, there is a need to eliminate lead from these glasses for environmental reasons. There is also a need to provide reduction resistant passivation glasses when fired on semiconductors such as silicon and silicon carbide. Accordingly, there exists a need for improved compositions for passivation glasses that address the shortcomings of the previous passivation techniques.